reason for fluting appearance 6

[electricpete]

What is the mechanism that creates the particular appearance of fluting (when bearings are exposed to electrical damage) ?

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(2B)+(2B)' ?

 

[Skogsgurra]

Same as dirt road wash board pattern. Mechanical resonance. No relation (almost) to frequency or speed.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[electricpete]

Thanks. Surely there are other mechanical defects that cause similar mresonance vibration behavior. Is it the interaction of the resonant vibration with the current flow?

Parallel converations here:

http://maintenanceforums.com/eve/forums/a/tpc/f/3751089011/m/80620995173?r=22520026173#22520026173

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(2B)+(2B)' ?

 

[electricpete]

Also here:

http://maintenanceforums.com/eve/forums/a/tpc/f/3751089011/m/19320429863?r=77220929863#77220929863

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(2B)+(2B)' ?

 

[Skogsgurra]

I can see that the standard crap about frequency and speed is alive and kicking in the maintenance forum.

I was invited to GE HQ in Schenetady in february to talk about these things. The presentation I made is available here:

http://www.gke.org/presentationer/files/GE Bearings and their electric environment w O and E.pdf

and it was also recorded and is available live on the GE intranet for those that have access to it.

There is a reason why the text about "conventional wisdom" has the colour it has (brown).

The discharges create little craters in the raceways and these craters, when there are enough of them, reduce the surface hardness so that the balls (or rolls) start to bounce and gradually create the fluting pattern.

The whole thing starts as a "misty" pattern aka "frosting" and that pattern does not have any periodicity in the beginning. It is only when the balls start to bounce that a periodic pattern develops and gets stronger and stronger until you gave to replace the bearing - or until it fails catastrophically.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

gave = have

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[ScottyUK]

Thanks Gunnar - that is a useful reference.

 

[electricpete]

Thanks Gunnar.
I will file this with two other previous presentations of yours
“All” about EDM in bearings on one page
EDM – Physics and Reality

The part I still want to clarify....

The discharges create little craters in the raceways and these craters, when there are enough of them, reduce the surface hardness so that the balls (or rolls) start to bounce and gradually create the fluting pattern.

The whole thing starts as a "misty" pattern aka "frosting" and that pattern does not have any periodicity in the beginning. It is only when the balls start to bounce that a periodic pattern develops and gets stronger and stronger until you gave to replace the bearing - or until it fails catastrophically.

.. Surely there are other mechanical defects that create a variety of defects (poor lubrication, contamination of various sizes, skidding... etc), yet none of those gives the fluting. So maybe the story should include something to do with current flowing as the rolling elements bounce on the races? (that would make more sense to me).

Attached is excerpt from section 6.4 of "Solving Tribology Problems in Rotating Machines" that was attached in the other thread and also attached here. Yet another spin on the story ... a little tough to follow.


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(2B)+(2B)' ?

 

[electricpete]

Attached is excerpt from section 6.4 of "Solving Tribology Problems in Rotating Machines" that was attached in the other thread and also attached here. Yet another spin on the story ... a little tough to follow.

Forgot that... here it is

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(2B)+(2B)' ?

 

[Skogsgurra]

Comment to Pete:

Other failure types than EDM do not form an even hardness reduction. It is only the repeated discharge through the oil film that creates millions and billions of small craters and the corresponding hardness reduction (low temperature tempering in SKF parlance). And it is only when you have a reduced hardness that the ball/roller bouncing occurs. Other failure types create other defects in the raceway surfaces. It is only the smooth and "wide area" reduction in hardness that creates bouncing. Just like a dirt road and not a paved road shows a wash-board pattern. The dirt road corresponds, of course, to the surface-tempered raceway.

The paper that Pete refers to says:
"The passage of current causes local surface heating, which leads to lowtemperature
tempering, and accelerates formation of corrugations with time.

The pitch of corrugations on the roller tracks depends on the bearing
kinematics, the frequency of rotation, the position of plane of action of radial
loading, the bearing quality and the lubricant characteristics"

I agree (almost) totally. The "frequency of rotation" (speed in my world) does not seem to be very important - fluting can also be seen in bearings running at variable speed. Winders in paper industry is a good example. Fast winders spend most of their time accelerating and decelerating and they still show very characteristic fluting.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[waross]

Great thread. Thank you Gunnar. lps

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Thanks Gunnar. I learnt a few 'facts'. Now to beat my clients with them.

Muthu

http://www.edison.co.in

 

[macmckim]

Great information, thankyou.

Does anyone have comments or experiences with oil lubricated sleeve bearings issues that have not been insulated when powered by VFD's? Does the electrical discharges damage the babbit materials?

TIA

 

[squeeky]

If you make up a small brush from conductive material like a copper brade and attach one side to an occiloscope and the other to earth, and look for high frequency distortion by placing your "brush" on the shaft, that may tellyou it exists. If it does there are several products on the market that can assist. These range from rings containing carbon fibre bristles to spring loaded gold brushes . Which country are you in?

 

[Skogsgurra]

Welcome to the world of real problem solving, squeeky.
I see that you are new here. Browse the site. There are lots to be learned.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.